High-frequency tube structure



J. R. wooDYARD HIGH-FREQUENCY TUBE STRUCTURE Filed-Aug. 20, 1945 www Patented `an. 9, 1951 2,537,112 HIGH-FREQUENCY TUBE STRUCTURE John R. Woodyard, Garden'City, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application August 20, 1945, Serial N0. 611,636

9 Claims. 1

The present invention relates to high frequency apparatus, and more particularly' to high frequency electron discharge tube apparatus of the velocity modulation type using cavity resonators.

Known means for and methods of tuning and/or frequency modulating electron discharge tube devices of the velocity modulation type have ing one or more cavity resonators suffer from one or the other, sometimes both, of the following defects. In the first place, electrical tuning by conventional methods, such as by varying the electron beam voltage, or by changing the reflector electrode voltage (in electron discharge tubes of the reex type) ,yield only a small amount of frequency shift, usually of the order of magnitude of one percent or less. If attempt is made to increase the electrical tuning range by altering the tube design, the efficiency of operation is considerably reduced because the known methods of electrical tuning are not actually tuning at all, but, rather are merely metho-ds of forcing the cavity resonator to oscillate off its natural frequency. These methods cannot change the frequency by more than approximately l/Q.

Secondly, methods of varying the frequency of such velocity modulation electron tube devices which force the cavity resonator to oscillate appreciably olf its natural frequency, also suffer the disadvantage that these methods vary the afsplitude' as well as the frequency of the electromagnetic energy output, since the resonator is then operating down from the peak of its resonance curve as soon as the frequency departs from the resonant frequency. These defects can be overcome substantially only by changing the natural frequency of the cavity resonator.

Certain known types of mechanical tuning, as by deforrning the resonator dimensions and/or shape or by inserting and moving conducting bodies within the resonator, do change the natural frequency of the resonator and, therefore, furnish a relatively large tuning range free from amplitude modulation. However, mechanical tuning, in general, suffers from the disadvantage that it is not readily applicable for use in frequcncy modulation, especially when the modulation signal voltage is of very high frequencies, such as are encountered in television or related arts. Such tuning is also awkward to use in automatic frequency control systems. The inapplicability of mechanical tuning is, to a large extcnt, due to the inertia of the moving parts. It has been shown by J P. Blewett and S. Ramo, in the Journal of Applied Physics, 1941, that an electron cloud or space charge which is caused to rotate about an axis of gyration by the action tion of the cloud and, hence on the magnitude of the forces involvedin producing the rotation of the electron cloud. If the electron cloud rotation is produced by a magnetic field oriented at right angles to an electric field and to the direction of electron emission, the variation of the dielectric constant of the space occupied by the rotating cloud is dependent on the strengths of the magnetic and electric fields. The dielectric constant thus obtainable is less than that of free space and may have values ranging from unity to zero or even negative values. Y

In accordance with the present invention, it is proposed to provide, in the cavity resonator of electron discharge devices of the velocity modu-7 lation type, electrical tuning means which employ the variable dielectric constant characteristic of a rotating space charge. It is further contemplated to obtain arelatively wide range of electronic tuning by adjustably controlling the strength of the magnetic eld, or by adjustably controlling the strength of the electric field or by simultaneously adjustably controlling both the magnetic and the electric field strenghs to which the space charge is exposed.

Accordingly, it is a principal object of the present invention to provide electronic means for and a method of rendering the natural oscillation frequency of cavity-type resonators in velocity modulation electron discharge tube devices continuously variable and adjustable over a relatively wide range of frequencies.

Another object of the present invention is to provide a high frequency electron discharge tube structure, wherein a wide range of tuning is made available through the application of a rotating space charge maintained within the cavity resonator of said structure.

Still another object of the present invention is to provide a high frequency electron discharge tube device having electronic means for tuning said device, which means are substantially free of amplitude effects, thus rendering said tuning means especially useful in frequency modulation devices.

A feature of the present invention resides in the provision of an electron space charge in the cavity resonator of a velocity modulation type of electron discharge tube and means including a uniform magnetic eld for rotating said space charge at a predetermined angular velocity,

booying novel Ieatures and principles, 'adapted i for use in other nelds.

Other objects and advantages will become apparent from the specification, taken in `connecr tion with the accompanying drawings wherein preferred embodiments or' the invention are illustrated.

in the drawings, Y "rig. 1 'is a longitudinal sectional View of a high frequency electron discharge tube embodying the invention;

Fig. 2 is a sectional View taken along the line 2-2 of Fig. 1; and A Fig. 3 is a iragmentary view of a modified form oftheuinvention. y U y Referring particularly to Figs. 41 and 2 there is shown an electron discharge tube structure of the velocity modulation type commonly known as a'Klystron. For the purpose of the present description only, and, without intending to be limited thereto, the present invention has been embodied in a rei-lex type of Klystron whose fundamental theory of operation is similarto that described With respect to Fig. 2 of United States Letters Patent No. 2,250,511, issued July 29, 1941, to Russell H. Varian and William W. Hansen, for Oscillator Stabilization System. It will be understood, however, that the-present invention is not limited to use in reflex Klystrons since it may be employed with equally satisfactory results in other types of velocity modulation devices such as any of the many forms of multiple resonator Klystron'oscillators, amplifiers, frequency-multipliers, etc.

The improved reflex Klystron illustrated in Figs. '1 and 2 comprises a cylindrical evacuated resonator shell I I havingV opposed rigid end walls I3 and I5 that are centrally apertured for `the purpose of receiving and mounting thereat -a tubular reentrant portion I1 vand la tubular pedestal I9, respectively.

The reentrant portion I1 extends through the opening in wall I3 coaxially with shell II and is terminated within said shell I I at a point closely spaced from wall I5 in a perforated grid 'structure 2| spaced from and parallel to a Similar'grid structure 23 mounted in the aperture of wall I5.

For providing a well-defined beam 'of electrons, there is mounted within the .pedestal I9'acath- `ode structure comprising an 'indirectly heated cathode 25having`a l'amentary heater 21 eX'- 4cited fro'm'a lament transformer 29through a vacuu'mseale'd base `structure 3|. The primary winding 'of transformer 29 may be energized from any suitable current source (not shown). ACa'th- 'ode `25 is shown provided with a collimating shield 353 for collim'atingthe electron -beam to di- Vr'ecttl'iesame throughthe Valigned grids 2 I, 273.

re'iiector plate 35 is coaxially supported within the reentrant portion I1 by'mean's of `conducting rod 31 which, "in turn, is vacuumsealed in insulation cap seal 39 provided at the outer end or' reentrant portion I1. A difference or potential between cathode 25 and reflector 35 is maintained by a battery 4I. If desired, the potential or' the reiiector 35 with respect to the cathode 25 may be made either positive or negative by means of a voltage-dividing variable tap arrangement shown at'43. A relatively high accelerating voltage from a high voltage source 45 is applied between the cathode 25 and grid 23 by connecting one terminal of the source 45 to `tlietube wallandthe other terminal to the cathode lead, as shown. So connected, grid 23 serves as an anode toi attracting electrons emitted from cathode 25. p

As thus far described, the reflex Klystron herein disclosed is of conventional design and operation. The electron stream from the cathode initially traverses the gap between resonator grids 2I 23 and is Vthen returned by reflector 35 into the resonator "I'I so as to exciteand maintain an oscillatory electromagnetic eld therein. Accepted 'theories'of this action 'based on 4electron'velocitymodulation principles are explained kfully in the above-mentioned Patent No. 2,250,511, to which reference is made for further details. -Ult'ra-l'iig'h frequency energy is extr'acted'fro'rn the'r'esonator l'field as by the usual concentric line terminal assembly 41.

,"To provide for an electronic space-'charge or cloud ywithin the -'resonator shell I I, van auxiliary indirectly heated cathode lstructure is provided comprising ya ,heater conm/I9Y iofminsulatekd ywire closely wound between iivalls 5I, '53 of `a double- Walled metallic cylinder 55. A coating 51 of electron emitting -material is suitably vapplied over the exterior suriace of the outer wall 5I of the cylinder y55. The heater coil I9 and the cylinder `55 assembly is preferably mounted coaxially with the reentrant portion I1, as shown, to minimize distortion ofthe resonator eld, being slightly spaced from the portion I1 and supported in "position by a metallic tube 59` rigidly fastened-to cylinder 55 around a suitable opening therein. Tube 59, in addition to its supporting action, forms -the inner conductor of a coaxial line4 terminal structure having an outer `conductor 5Iv rigidly 'securedto or integral with the end wall I3 of shell I I. Wire 49 may convenient- -ly be brought Eout of the resonator space and connected to one terminal of a heater battery y63 by running it up-through'the interior of tubular inner conductor l59. The other end of wire ll9'maybe spot Welded vto the-double-walled cylinder 55 "as at65. Theh'eater -supply circuit for lwire '4'9-is` c'omplet'edvbyi connecting the other terminal-of battery 53 to'tubular'inner'conductor Y59, as'illustrated. Filter sections 61, 69 formed as quarter-Wavelength lengths of coaxial transmission line are provided to isolate the vheater current circuit from the high frequencyenergy contained within -the resonator.

VlFor attracting electrons-emitted from the Yauxvili'arybathode, anop'neended cylindrical auxillary anode 1I is mounted radially'spaced fromand `coaxially supported with respect to ythe auxiliary cathode 'supporting cylinder Y55 by means of a 'rigidi'conductng rod 13, which, in combination 'tubular outer conductor 15 secured to resonator I I, rforms a coaxial 1ine`terminal structure having '-quarter-Jwavelength coaxial transmission Vline riilt'ersections V11, 19 useful 'to inhibit leaklage of h iglifreguency energy from the resonator. 'A positive potential 'is maintained on lanode v1I si relative to the auxiliary cathode by means of variable-voltage battery 8| which is connected to said anode 1I through the secondary winding of an input transformer 83 and the coaxial line filter sections 11, 19.

During the course of travel from cathode emitter surface 51 to anode 1|, the electrons are forced to traverse spiral paths by an axial magnetic field produced by a coil 85 of which the windings are suitably connected to a Variable energizing battery 81. To concentrate the magnetic field produced by the coil 85, a soft iron shell 89 is provided having poles'as at 9| and 93. If desired, the electromagnet may be replaced by a permanent magnet with variable shunt, for the same purpose.

Fig. 3 shows a considerably simplified modification of the present invention. In place of the type of auxiliary cathode hereinabove described, a simplified cathode structure is provided comprising a coating 95 of electron emitting material applied directly to the outer-surface of the reentrant portion I1 and a heater coil 91 is mounted interiorly and coaxially of said reentrant portion I1, the heater leads being brought out, as wires 99, through seal 39. If desired, a cylindrical jacket may be mounted interiorly of Said reentrant portion |1 and coil 91 to serve as a heat shield for directing the heat from coil 51 toward the coating 95. By this construction, the use of separate high frequency filter circuits 81, 69 (Fig. 1) for the auxiliary cathode and anode structures is obviated inasmuch as the space within reentrant portion .I1 is free from high frequency fields.

Also, anode 1|, shown in the embodiment of Figs. 1 and 2, may be eliminated as a separate structure within the resonator shell and, in place thereof, the cylindrical wall of the resonator II may be employed, being insulated from the pole I1. Thus, a positive potential from variable voltage source |02 may be applied to the resonator side wall relative to the auxiliarycathode through a suitable radio frequency filter arrangement IIlI for minimizing leakage of high frequency energy from the resonator. If desired, more elaborate filters such as quarter-wave sections can be used in place of filter IDI. It will be observed, that, by using the simplified auxiliary cathode construction described above together with the resonator side wall as the anode, a rotating space charge may be provided without introducing any auxiliary electrodes into the resonator space.

It has been found that the presence of sepa-.- rate auxiliary cathode and anode structures of the type shown in Figs. 1 and 2, in the resonator reduces it Q by only an inconsequential amount, approximately -20%. This relatively low reduction in Q is, in a large measure, due to the fact that the auxiliary electrodes are placed so that metal surfaces thereof are approximately perpendicular to the high frequency field, as shown in Fig. 1, and that said electrodes are supported by the quarter wave lters 61, 69 and 11, 19. It will be understood that any number of such filter supports may be used as are mechanically desirable.

In operation, the electronically tuned tube in either of the herein disclosed modified forms is normally permitted to function in accordance with the mode and principles of operation set forth in the above-mentioned Patent No. 2,250,511. For obtaining a wide range of tuning, the voltage of battery 81 is varied, producing corresponding variations in the strength of the mag' netic field and thereby varying the angular velocity of rotation of the space charge or cloud of electrons produced by the auxiliary electrodes. The variations of angular velocity of the cloud produce corresponding alterations in the dielectric constant of the resonator space, thus changing the natural resonant frequency of the resonator and the oscillatory electromagnetic eld associated therewith.

Frequency changes of the resonator are also obtainable by Varying the strength of the radial electric field between the auxiliary cathode and anode as by'varying the voltage of battery 8 I. It has been observed that, to obtain the widest possible tuning range, batteries 81 and 8| may both be varied together, in proper ratio.

For wide band frequency modulation, I propose to apply a signal voltage in series with the battery 8| voltage by means of transformer 83, as shown. Alternatively, the frequency modulation signal voltage may be applied in series with battery 81 by means of transformer |03, or in both places simultaneously.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings Shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. Apparatus for generating electromagnetic energy adjustable over a Wide range of ultrahigh frequencies, comprising electron-beam producing means comprising a cathode and means for focusing electrons emanating from said cathode into a beam of predetermined cross-section; hollow conductive means adapted to contain a dielectric medium for sustaining an oscillating electromagnetic i'leld at a resonant frequency of said medium to act on said beam of electrons, said conductive means comprising parallel, closely spaced perforate portions in the path of the electrons of said beam, a tubular reentrant portion extending from one of said perforate portions and surrounding the path of said beam and an annular wall portion extending from adjacent said tubular portion to the other perforate portion deflning an annular cavity adapted to sustain an' oscillating electromagnetic field such that a substantial component of the electric fleld will appear between said perforate portions; a reflector electrode disposed in the path of the electron beam and spaced from said cathode beyond said perforate portions to reflect said electron beam after its passage through said perforate portions whereby said electron beam is enabled to excite the electromagnetic eld within said dielectric medium, an annular second cathode coaxial with and at least partially surrounding said reentrant portion, anode means likewise coaxial with and at least partially surrounding said reentrant portion and radially spaced from said annular cath- 0de for maintenance of a 110W of electrons from said annular cathode toward said anode means, magnetic-field-producing means disposed adjacent said wall portion and adapted to produce a magnetic field relatively strong within and substantially parallel to the axis of the space between the annular cathode and said anode means, whereby electrons from the annular cathode are caused to move in spiral paths, and means coupled to at least one of said magnetic-neld-proessaim ducing' meansand said anode means for adjusting the relation vbetween the strength of the magnetic iield and the potential between said anode means and said annularcathode to vary the frequency .of the electromagnetic field.

2. Ultra-high-frequency apparatusadjustable over a wide range of frequencies, I comprising means for producing a beam of electrons, a cavity resonator .having parallel, closely spaced, perforate portions disposed along thepath of said beam, said resonator also having *al tubular reentrant portion extending from o-ne of saidperforate portions and surrounding said beam path andan outer wall portionconnecting said tubular portion to the other of said perforate portions to define an annular cavity adapted tocontain an electromagnetic iield to interact with said' beam, an annular cathode coaxial withland at least partially surrounding said reentrant portion, anode means likewise coaxial with and at least partially Y surrounding said reentrant lportion and radially spaced from said cathode for maintenance of a flow of electrons from said .annular cathode toward said anode means, magnetic-field-producing means disposed adjacent said outer wall portion and adapted to produce a magnetic eld within said resonator and substantially parallel to the axis of said cathode and said anode means, and means coupling a potential source between said cathode and said anode means whereby electrons from said annular cathode are caused tomove in spiral paths, and means vcoupled to at least one of said magnetic field producing means and said anode means for adjusting the relationbetween the strength of said magnetic eld and the potential between anode and cathode, whereby the resonant frequency of the resonatormay be varied.

3. In a velocity modulation tube for producing ultra-high frequency energy, conductive means defining a hollow cavity resonator enclosing la space in which kan electrical iield may resonate, said resonator including -a pair of electronpermeable walls positioned in mutually spaced relation, means including a cathode substantially aligned with said `electron-permeable walls for passing a beam of electrons therethrough, means for producing a second electric ield including a second cathode for producing a second electron stream in the space in said resonator in which the rst-mentioned electrical iield-may resonate, magnetic held-producing means for producing a magnetic field in said resonator having a direction substantially normal to the direction of said second electric iield and substantially parallel to the direction of said iirst beam'of'electrons, and means coupled to at least -one -of said field-producing means for varying the strength thereof relative to the other whereby the frequency of the resonating electrical ield in said resonator may bevaried.

4. In a ve..ocity modulation tube for producing ultra-high-frequency energy,A conductive means defining a hollow cavity resonator enclosing a space in which an electrical iield `may resonate, said resonator including a pair of electron-permeable walls positioned in mutually spaced relation, means including -a'cathode substantially aligned with said electron-permeabe walls for passing a beam of electrons therethrough, means for producing a second electric iield including a second cathode disposed within the cavity resonator and adapted to produce a second electron stream in the space therewith'n, magnetic Ifieldproducing means for producing a magnetic iield in saidresonatorfhaving-.afdirectionisubstantially' normal tothe direction of v-saidlsecond electric el'd land substantiallyparallel.to the direction of said first beam of electrons,-and means coupled to at least one of said field-producing means forvarying the 'strength thereof relative to the other wherebythe frequency of the resonating electrical 'iield in said vresonator may be varied.

'-5. Ink a velocity modulation: tube for producing ultra-high-frequency energy, conductive means defining la hol-low'cavity resonatorenclosing a space lin which .an velectrical eld `may resonate, said resonator including-a pairof electron-permeable walls' positioned inmutuallyispaced relation, means including a cathode substantially aligned with said electron-permeable walls for passing a beam of electrons therethrough,r means for producing a second electric iiefd, including a secondcathode .disposed within said cavity resonator and arrangedA in concentric relation to the beam vof electrons produced by the rst mentioned cathodefsalid second l.cathode vbeing adapted to produce la second electron stream in the space within said resonator, magnetic fied-producing means for producingfa magnetic field in said resonator having a direction substantially normal to the direction yof said second electric field and substantially parallel to the direction of said iirst'beam of electrons, and means coupled to at least yone of said field-producing means for varying the strengththereof Vrelative to the other wherebythe frequency v:of the resonating electrical ield .in said resonator may be varied.

6. In1a velocity .modulationtube for producing ultra-high-frequency energy, conductive means `defining a `hollow/:cavity resonator enclosinglaspace vin whichan electrical eld `may resonate, said resonalor including a pair of electronpermeable walls-positioned in-mutually spaced relation, means :including a cathode substantially aligned rvwith said electron-permeable walls for passingra beam of electrons therethrough, means for producing la second electric field including `a second `cathode ydisposed within said cavitycresonator and :in concentric relation to -the beam of electrons produced by the Yfirst mentioned-cathodel for :producing a'second electron stream substantially perpendicular to vsaid rst electron beam, -magnetic eld-producing means for producinga magnetic liield in said-resonator 4having aadirectionsubstantially paralleling the velectron beam produced by the irstmentioned cathode, and means-coupled .to Aat least one -of-said fieldproducing means for varying the strength thereof relative to the -other' whereby the frequency of the resonating` electrical eld -in said resonator maybe varied.

7. Ina velocitymodula-tion tube for producing ultra-hight-.frequency energy, .conductive means dening a hollow cavity resonator enclosing a spacelin `which yan electrical field may resonate, said resonator yincluding a pair of electron-,permeablewalls positioned rin `mutually spaced relation, kmeansincludingua cathode substanaially aligned withffsaid electron-permeable walls for passing a-beamof` electrons therethrough, means for producinga-second electric held-including a second cathode of annular configuration disposed within said cavity resonator and in *concentrici relation to 'the electron beam produced by the first mentioned cathode, the direction of the electron stream produced by said second cathode ybeing substantially lperpendicular to the direction of said first beam of electrons,an annular anode disposed within said-cavity resonator in spaced,

concentric relation t said second cathode, magnetic field-producing means for producing a magnetic field in said resonator having a direction substantially normal to the direction of the second electric field and substantially paralleling the electron beam produced by the rst mentioned cathode, and means coupled to at least one of said field producing means for varying the strength thereof relative to the other whereby the frequency of the resonating electrical field in said resonator may be varied.

8. Ultra-high-frequency apparatus adjustable over a wide range of frequencies, comprising means for producing a beam of electrons, a cavity resonator having parallel, closely spaced, perforate portions disposed along the path of said beam, said resonator also having a tubular reentrant portion extending from one of said periorate portions and surrounding said beam path and an outer wall portion connecting said tubular portion to the other of said perforate portions to define an annular cavity adapted to contain an electromagnetic field to interact with said beam, an annular cathode coaxial with and atV least partially surrounding said reentrant portion, anode means likewise coaxial with and at least partially surrounding said reentrant portion and radially spaced from said cathode for maintenance of a flow of electrons from said annular cathode toward said anode means, means disposed adjacent said resonator for producing a magnetic field within said resonator and substantially parallel to the axis of said cathode and said anode means, means coupling a potential source between said cathode and said anode means whereby electrons from said annular cathode are caused to move in spiral paths, and means coupled to at least one of said magnetic eld producing means and said anode means for adjusting the relation between the strength of said magnetic field and the potential between anode and cathode, whereby the resonant frequency of the resonator may be varied.

9. Ultra-high-frequency apparatus adjustable over a wide range of frequencies, comprising means for producing a beam of electrons, a cavity resonator having parallel, closely spaced, perforate portions disposed along the path of said beam, said resonator also having a tubular reentrant portion extending from one of said perforate portions and surrounding said beam path and an outer wall portion connecting said tubular portion to the other of said perforate portions to define an annular cavity adapted to contain an electromagnetic field to interact with said beam, a reflector electrode disposed adjacent said resonator and in the path of said beam on the side of said resonator opposite said electron beam producing means, an annular cathode coaxial with and at least partially surrounding said reentrant portion, anode means likewise coaxial with and at least partially surrounding said reentrant portion and radially spaced from said cathode for maintenance of a flow of electrons from said annular cathode toward said anode means, means disposed adjacent said resonator for producing a magnetic field within said resonator and substantially parallel to the axis of said cathode and said anode means, means coupling a potential source between said cathode and said anode means whereby electrons from said annular cathode are caused to move in spiral paths, and means coupled to at least one of said magnetic lield producing means and said anode means for adjusting the relation between the strength of said magnetic eld and the potential between anode and cathode, whereby the resonant frequency of the resonator may be varied. JOHN R. WOODYARD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Brown Mar. 8, 1949 

